Frap Tools Sapel - Tamed Random Source
sapel / sa'pe:l / s.m. [dialect from the northern area of Modena - Italy, uncertain etymology: probably from vulgar Latin sappa, 'hoe', meaning roughly hoe'd] - 'mess', 'muddle','chaos'.
The Sapel is a random control voltages source for Eurorack modular systems. It is composed of two main sections, one that generates audio noises, in 4 different versions, and another which includes two specular random clock, random voltages and clock sources.
Noise outputs are colour coded, based on the noise colours and include
• Blue (+3dB / oct spectrum
• White noise (0dB / oct spectrum)
• Pink noise (-3dB / oct spectrum)
• Red noise, aka brown or brownian (-6dB / oct spectrum)
The random voltage and clock section features four uncorrelated random CV generation paths, divided in:
• Fluctuating random voltage
• Quantized random voltage with 2n stages tuned in semitones referred to 1v / oct scale
• Quantized random voltage with n+1 stages tined in octaves referred to 1v / oct scale
• Non-quantized sample & hold
It is also possible to set a probability distribution with a potentiometer and apply (or do not apply) the chosen distribution setting to each of the four paths independently.
Furthermore, each of the two random sources section features an independent built-in clock generator, with clock output and random clock output, which can be used in 'more than' or 'less than' mode. It is possible to use an external clock signal as a clock source, bypassing the built-in one. In addition to that, it is also possible to hand trigger the clock via a manual sample & hold button, which can be also modulated by gate signals.
Two analog true-random modules in one
Sapel has two analog sample-and-hold circuits that generate eight random voltages simultaneously from analog thermal noise.
Each circuit has its own internal clock, which you can override with external trigs.
Versatile Clock and Triggering circuit (yes, with buttons)
You can trig the four random generators in four ways:
• With the internal clock
• With external trigs (overriding the internal clock)
• With external signals (without overriding the internal clock)
• With the built-in button
You can also modulate the internal clock's rate externally.
Each random generator has a clock output and a Random clock output.
In Less Than mode, the Random clock outputs just some clocks here and there.
In More Than mode, it outputs more random clocks than the main one.
In both cases, the Global Rate of Change defines the random clock density.
Quantized Random Voltages (Revisited)
The 2n circuit generates random voltages precisely tuned to 12-EDO semitones.
The n+1 circuit outputs random voltages quantized to octaves.
Both circuits' knobs define the n value, from 1 to 6: in this way, the 2n section can output 2, 4, 8, 16, 32 or 64 semitones, while the n+1 circuit can output 2, 3, 4, 5 ,6 or 7 octaves.
Frap Tools, of course, drew from the classic Buchla 266 but redesigned the circuit from scratch to provide a more even and 'musical' value distribution.
Fluctuating Random Voltages (and Global Rate of Change)
This circuit generates a smooth, fluctuating random voltage.
It is the only random output that is not linked to the clock. It is a separate S&H circuit that integrates its values.
Its knob defines the fluctuation rate, from subtle to LFO-like frequencies to a sort of audio noise.
The Fluctuating Random knob also defines the random clock probability (Global Rate of Change).
True Unquantized S&H
Each generator has a classic, unquantized S&H circuit. It's wide range and its all-analog generation guarantee true noise: you won't get two similar voltages in a row for a while.
The Colours of Noise
Sapel also has four analog noise outputs that provide Blue, White, Pink and Red noise.
Hissing cymbals, roaring thunders and windy seashores are at your fingertips
Tame Your Randomness: Probability Distribution
This circuit allows you to control the average random voltage magnitude. From left to right, it will make the S&H circuits generate more low, mid or high values, respecitively.
On each section, you can route the Probability Distribution to each of the four random noise generators independently.